Cooling systems for cooling turbine blades in gas turbine engines often employ a pre-swirl arrangement to reduce the temperature of the cooling air and to accelerate the cooling air before it is fed to the turbine blade mounting disc for blade cooling. Acceleration of the cooling to a speed approaching or equal to the rotational speed of the rim of the blade mounting disc minimises aerodynamic losses as the cooling air is transferred from the static structure of the gas turbine engine to the rotating engine components.
Acceleration of the cooling air creates a pressure loss in the pre-swirl arrangement and, consequently, other air flows within the gas turbine engine may contaminate the cooling air flow provided by the pre-swirl arrangement.